The present invention deals with reading data from a magnetic disk. More particularly, the present invention deals with adjusting window center settings in a read channel of a magnetic disk drive
A magnetic disk, such as one used in a computer disk drive, is a flat circular platter with a magnetic surface. Data is stored on the magnetic surface by selective polarization of portions of the magnetic surface. The presence or absence of polarity transitions between the polarized portions represents particular binary values. Typically, the magnetically polarized portions are arranged in a plurality of radially concentric tracks on the magnetic surface to aid in location and read back of the data.
In order to read back the data recorded on the magnetic surface, a magnetic transducer moves relative to the magnetic disk along a given track. The magnetic transducer generates an electrical signal (the "read signal"), which represents the states of polarization encountered along the track. Pulses in the read signal correspond to the magnetically polarized portions of the magnetic disk.
Ideally, the read signal would not be influenced by any factors other than the magnetically polarized portions. However, other factors do influence the read signal and must be taken into account in processing the read signal.
During processing of the read signal, the processing logic (i.e. the read chain logic) is configured to recover data from the read signal during a certain period in time known as a read window. The read window represents the time during which the pulses in the read signal, which represent digital data stored on the magnetic disk, are valid. However, the actual window during which the pulses are valid can shift in time due to aging of the circuitry in the magnetic disk drive. Also, as the circuitry heats up during operation, the temperature differential can cause the read window to shift. Further, the optimum read window can shift due to process changes in the magnetic disk drive or due to part-to-part timing variation in the read chain circuitry of the magnetic disk drive.